<!-- Installing Go -->

<h2>Introduction</h2>

<p>Go is an open source project, distributed under a
<a href="/LICENSE">BSD-style license</a>.
This document explains how to check out the sources,
build them on your own machine, and run them.
</p>

<p>
There are two distinct ways to experiment with Go.
This document focuses on the <code>gc</code> Go
compiler and tools (<code>6g</code>, <code>8g</code> etc.).
For information on how to use <code>gccgo</code>, a more traditional
compiler using the GCC back end, see
<a href="gccgo_install.html">Setting up and using gccgo</a>.
</p>

<h2>Environment variables</h2>

<p>
The Go compilation environment depends on three environment variables plus one optional variable:
</p>

<dl>
<dt>
	<code>$GOROOT</code>
</dt>
<dd>The root of the Go tree.  Typically this is <code>$HOME/go</code>
	but it can be any directory.
</dd>

<dt>
<code>$GOOS</code> and <code>$GOARCH</code>
</dt>
<dd>
	The name of the target operating system and compilation architecture.
	Choices for <code>$GOOS</code> are <code>linux</code>,
	<code>freebsd</code>,
	<code>darwin</code> (Mac OS X 10.5 or 10.6),
	and <code>nacl</code> (Native Client, an incomplete port).
	Choices for <code>$GOARCH</code> are <code>amd64</code> (64-bit x86, the most mature port),
	<code>386</code> (32-bit x86), and
	<code>arm</code> (32-bit ARM, an incomplete port).
	The valid combinations of <code>$GOOS</code> and <code>$GOARCH</code> are:
	<p>
	<table cellpadding="0">
	<tr>
	<th width="50"><th align="left" width="100"><code>$GOOS</code></th> <th align="left" width="100"><code>$GOARCH</code></th>
	</tr>
	<tr>
	<td></td><td><code>darwin</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>darwin</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>freebsd</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>freebsd</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>linux</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>linux</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>linux</code></td> <td><code>arm</code></td>
	</tr>
	<tr>
	<td></td><td><code>nacl</code></td> <td><code>386</code></td>
	</tr>
	</table>
	<p>
</dd>

<dt>
<code>$GOBIN</code> (optional)
</dt>
<dd>
	The location where binaries will be installed.
	The default is <code>$HOME/bin</code>.
	After installing, you will want to arrange to add this
	directory to your <code>$PATH</code>, so you can use the tools.
</dd>

<dt>
<code>$GOARM</code> (optional, arm, default=6)
</dt>
<dd>
	The ARM architecture version the runtime libraries should target.
	ARMv6 cores have more efficient synchronization primitives. Setting
	<code>$GOARM</code> to 5 will compile the runtime libraries using
	just SWP instructions that work on older architectures as well.
	Running v6 code on an older core will cause an illegal instruction trap.
</dd>
</dl>

<p>
Note that <code>$GOARCH</code> and <code>$GOOS</code> identify the
<em>target</em> environment, not the environment you are running on.
In effect, you are always cross-compiling.
</p>

<p>
Set these variables in your shell profile (<code>$HOME/.bashrc</code>,
<code>$HOME/.profile</code>, or equivalent). The settings might look 
something like this:
</p>

<pre>
export GOROOT=$HOME/go
export GOARCH=amd64
export GOOS=linux
</pre>

<p>
Double-check them by listing your environment. (You will need to launch
a new shell or terminal window for the changes to take effect.)
</p>

<pre>
$ env | grep '^GO'
</pre>

<h2>Ports</h2>

<p>
The Go compilers support three instruction sets.
There are important differences in the quality of the compilers for the different
architectures.
</p>

<dl>
<dt>
	<code>amd64</code> (a.k.a. <code>x86-64</code>); <code>6g,6l,6c,6a</code>
</dt>
<dd>
	The most mature implementation.  The compiler has an effective optimizer
	(registerizer) and generates good code (although <code>gccgo</code>
	can do noticeably better sometimes).
</dd>
<dt>
	<code>386</code> (a.k.a. <code>x86</code> or <code>x86-32</code>); <code>8g,8l,8c,8a</code>
</dt>
<dd>
	Comparable to the <code>amd64</code> port. Not as well soaked but
	should be nearly as solid.

</dd>
<dt>
	<code>arm</code> (a.k.a. <code>ARM</code>); <code>5g,5l,5c,5a</code>
</dt>
<dd>
	It's got a couple of outstanding bugs but is improving.
	Tested against QEMU and an android phone.
	Only supports Linux binaries.
</dd>
</dl>

<p>
Except for things like low-level operating system interface code, the runtime
support is the same in all ports and includes a mark-and-sweep garbage collector
(a fancier one is in the works), efficient array and string slicing,
support for segmented stacks, and a strong goroutine implementation.
</p>

<p>
See the separate <a href="gccgo_install.html"><code>gccgo</code> document</a>
for details about that compiler and environment.
</p>

<h2>Install C tools, if needed</h2>

<p>The Go tool chain is written in C.  To build it, you need
to have GCC, the standard C libraries, the parser generator Bison,
<tt>make</tt>, <tt>awk</tt>, and the text editor <tt>ed</tt> installed.  On OS X, they can be
installed as part of
<a href="http://developer.apple.com/TOOLS/Xcode/">Xcode</a>.  On Linux, use
</p>

<pre>
$ sudo apt-get install bison gcc libc6-dev ed gawk make
</pre>

<p>
(or the equivalent on your Linux distribution).
</p>

<h2>Fetch the repository</h2>

<p>
If you do not have Mercurial installed (you do not have an <code>hg</code> command),
this command:
</p>

<pre>
$ sudo easy_install mercurial
</pre>

<p>works on most systems.
(On Ubuntu/Debian, you might try <code>apt-get install python-setuptools python-dev build-essential gcc</code> first.)
If that fails, visit the <a href="http://mercurial.selenic.com/wiki/Download">Mercurial Download</a> page.</p>

<p>Make sure the <code>$GOROOT</code> directory does not exist or is empty.
Then check out the repository:</p>

<pre>
$ hg clone -r release https://go.googlecode.com/hg/ $GOROOT
</pre>

<h2>Install Go</h2>

<p>
To build the Go distribution, run
</p>

<pre>
$ cd $GOROOT/src
$ ./all.bash
</pre>

<p>
If all goes well, it will finish by printing
</p>

<pre>
--- cd ../test
N known bugs; 0 unexpected bugs
</pre>

<p>
where <var>N</var> is a number that varies from release to release.
</p>

<h2>Writing programs</h2>

<p>
Given a file <code>file.go</code>, compile it using
</p>

<pre>
$ 6g file.go
</pre>

<p>
<code>6g</code> is the Go compiler for <code>amd64</code>; it will write the output
in <code>file.6</code>. The &lsquo;<code>6</code>&rsquo; identifies
files for the <code>amd64</code> architecture.
The identifier letters for <code>386</code> and <code>arm</code>
are &lsquo;<code>8</code>&rsquo; and &lsquo;<code>5</code>&rsquo;.
That is, if you were compiling for <code>386</code>, you would use
<code>8g</code> and the output would be named <code>file.8</code>.
</p>

<p>
To link the file, use
</p>

<pre>
$ 6l file.6
</pre>

<p>
and to run it
</p>

<pre>
$ ./6.out
</pre>

<p>A complete example:
</p>

<pre>
$ cat &gt;hello.go &lt;&lt;EOF
package main

import "fmt"

func main() {
	fmt.Printf("hello, world\n")
}
EOF
$ 6g hello.go
$ 6l hello.6
$ ./6.out
hello, world
$
</pre>

<p>
There is no need to list <code>hello.6</code>'s package dependencies
(in this case, package <code>fmt</code>) on the <code>6l</code>
command line.
The linker learns about them by reading <code>hello.6</code>.
</p>

<p>
To build more complicated programs, you will probably
want to use a
<code>Makefile</code>.
There are examples in places like
<code>$GOROOT/src/cmd/godoc/Makefile</code>
and <code>$GOROOT/src/pkg/*/Makefile</code>.
The
<a href="contribute.html">document</a>
about contributing to the Go project
gives more detail about
the process of building and testing Go programs.
</p>

<h2>Keeping up with releases</h2>

<p>New releases are announced on the <a href="http://groups.google.com/group/golang-nuts">Go Nuts</a> mailing list.
To update an existing tree to the latest release, you can run:
</p>

<pre>
$ cd $GOROOT/src
$ hg pull
$ hg update release
$ ./all.bash
</pre>

<h2>Community resources</h2>

<p>
For real-time help, there may be users or developers on
<code>#go-nuts</code> on the <a href="http://freenode.net/">Freenode</a> IRC server.
</p>

<p>
The official mailing list for discussion of the Go language is
<a href="http://groups.google.com/group/golang-nuts">Go Nuts</a>.
</p>

<p>
Bugs can be reported using the <a href="http://code.google.com/p/go/issues/list">Go issue tracker</a>.
</p>

<p>
For those who wish to keep up with development,
there is another mailing list, <a href="http://groups.google.com/group/golang-checkins">golang-checkins</a>,
that receives a message summarizing each checkin to the Go repository.
</p>


